Systems and methods for improved digital rf transport in distributed antenna systems

ABSTRACT

Systems and methods for improved digital RF transport in a DAS are provided. In one embodiment, a transceiver comprises: a receive path circuit including an RF reception interface coupled to an ADC, the ADC receiving a down-converted analog RF spectrum from the RF reception interface and producing a digitized RF spectrum at an input sampling rate; a logic device receiving the digitized RF spectrum and producing a first set of baseband data samples at a first sampling rate, corresponding to a first spectral region of the analog RF spectrum and a second set of baseband data samples at a second sampling rate, corresponding to a second spectral region of the analog RF spectrum. The logic device maps the first set and second sets of baseband data samples to a respective first set and second set of timeslots of a serial data stream transport frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/144,349, filed on Jan. 13, 2009, which is incorporated herein byreference in its entirety.

BACKGROUND

A Distributed Antenna System (DAS) is a network of spatially separatedantenna nodes connected to a common node via a transport medium thatprovides wireless service within a geographic area or structure. Commonwireless communication system configurations employ a host unit as thecommon node, which is located at a centralized location (for example, ata facility that is controlled by a wireless service provider). Theantenna nodes and related broadcasting and receiving equipment, locatedat a location that is remote from the host unit (for example, at afacility or site that is not controlled by the wireless serviceprovider), are also referred to as “remote units.” Radio frequency (RF)signals are communicated between the host unit and one or more remoteunits. In such a DAS, the host unit is typically communicatively coupledto one or more base stations (for example, via wired connection or viawireless connection) which allow bidirectional communications betweenwireless subscriber units within the DAS service area and communicationnetworks such as, but not limited to, cellular phone networks, thepublic switch telephone network (PSTN) and the Internet. A DAS canprovide, by its nature, an infrastructure within a community that canscatter remote units across a geographic area for providing wirelessservices across that area.

A digital DAS is a system wherein the host unit and remote unitstransport radio signal information to one another by digital means (forexample, by digitally sampling a wireless radio frequency (RF) spectrumat a remote unit and transmitting the digital sample data to the hostunit by fiber optics). One problem with the digital DAS occurs whenradio signals of interest within the RF spectrum are separated bybandwidths containing no signals interest. In that case, fiber bandwidthwithin the digital DAS is wasted because all of the digital samples needto be transported at a rate sufficient to cover the full range offrequencies, not just the portions containing signals of interest.

For the reasons stated above and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the specification, there is a need in the art for improvedsystems and methods for digital RF transport.

SUMMARY

Systems and methods for improved digital RF transport in a DAS areprovided. In one embodiment, a transceiver comprises: a receive pathcircuit including an RF reception interface coupled to an ADC, the ADCreceiving a down-converted analog RF spectrum from the RF receptioninterface and producing a digitized RF spectrum at an input samplingrate; a logic device receiving the digitized RF spectrum and producing afirst set of baseband data samples at a first sampling rate,corresponding to a first spectral region of the analog RF spectrum and asecond set of baseband data samples at a second sampling rate,corresponding to a second spectral region of the analog RF spectrum. Thelogic device maps the first set and second sets of baseband data samplesto a respective first set and second set of timeslots of a serial datastream transport frame.

DRAWINGS

Understanding that the drawings depict only exemplary embodiments of thepresent invention and are not therefore to be considered limiting inscope, the exemplary embodiments will be described with additionalspecificity and detail through the use of the accompanying drawings, inwhich:

FIG. 1 is a block diagram of a distributed antenna system of oneembodiment of the present invention;

FIG. 2 is a block diagram of a remote unit of one embodiment of thepresent invention;

FIG. 3 is a block diagram of a host unit of one embodiment of thepresent invention;

FIGS. 4A-4C illustrate mapping of RF spectral regions to transport frametimeslots, of one embodiment of the present invention;

FIG. 5 is a block diagram illustrating a DART Module of one embodimentof the present invention;

FIG. 6 is a block diagram illustrating an FPGA configuration for a DARTModule of one embodiment of the present invention;

FIG. 7 is a flow chart illustrating a method of one embodiment of thepresent invention;

FIG. 8 is a flow chart illustrating a method of one embodiment of thepresent invention; and

FIG. 9 is a flow chart illustrating a method of one embodiment of thepresent invention.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize features relevant to thepresent invention. Reference characters denote like elements throughoutfigures and text.

DETAILED DESCRIPTION

Embodiments of the present invention address the problem of efficientlytransporting multiple non-adjacent communications bands within thedigital transport of a distributed antenna system. This is accomplishedby segregating from a digitized RF spectrum a plurality of smallerspectral regions that include relevant signals of interest, anddiscarding information not within those spectral regions. Thissegregation further allows the spectral regions to be processedindependently, and each independently re-sampled (at a sampling ratebased on their respective bandwidths) so that they can be transmittedover a common serial transport link. Each spectral region is transmittedusing a number of timeslots in the serial bit stream that is a functionof their respective bandwidths rather than the bandwidth of the entiredigitized RF spectrum.

FIG. 1 is a block diagram of a distributed antenna system (DAS) 100 ofone embodiment of the present invention for receiving and distributingradio frequency signals within a coverage area. DAS 100 includes a hostunit 102 and a plurality of remote units 106. At the physical layer,host units 102 and remote units 106 are communicatively coupled via acommunication link 130 to form a bidirectional communication networkcomprising a plurality of point-to-point communication links 130. In oneembodiment, one or more of communication links 130 are fiber optic cableas indicated in FIG. 1. Optionally, host units 102 and remote units 106may be interconnected via coaxial cable, or a combination of bothcoaxial cable and fiber optic cable. Additionally, in other embodiments,one or more of communication links 130 are wireless millimeter wavelinks (e.g. E Band/70 GHz radio). Here a millimeter signal transceiveris coupled to host unit 102 and each remote unit 106 on each end ofcommunication link 130. In yet another embodiment, one or more ofcommunication links 130 a microwave radio links where microwave radiotransceivers are coupled to host unit 102 and remote units 106.

Remote units 106 each house electronic devices and systems used forwirelessly transmitting and receiving modulated radio frequency (RF)communications via antenna 107 with one or more mobile subscriber units108. Host unit 102 is coupled to at least one base transceiver station(BTS) 110 often referred to as a base station. BTS 110 communicatesvoice and other data signals between the respective host unit 102 and alarger communication network via a gateway 124 coupled to a telephonesystem network 122 (for example, the public switched telephone networkand/or wireless service provider networks) and an internet protocol (IP)network 120, such as the Internet. In one embodiment, DAS 100 comprisespart of a cellular telephone network and subscriber units 108 arecellular telephones. In alternate embodiments, BTS 110 and host unit 102may be interconnected via coaxial cable, fiber optic cable, wirelesscommunication links, or any combination thereof.

Downlink RF signals are received from the BTS 110 at the host unit 102,which the host unit 102 uses to generate one or more downlink transportsignals for transmitting to one or more of the remote units 106. Eachsuch remote unit 106 receives at least one downlink transport andreconstructs the downlink RF signals from the downlink transport signaland causes the reconstructed downlink RF signals to be radiated from aremote antenna 107 coupled to or included in that remote unit 106. Asimilar process is performed in the uplink direction. Uplink RF signalsreceived at one or more remote units 106 from subscriber 108 are used togenerate respective uplink transport signals that are transmitted fromthe respective remote units 106 to the host unit 102. The host unit 102receives and combines the uplink transport signals transmitted from themultiple remote units 106. The host unit 102 communicates the combineduplink RF signals to the BTS 110 over a broadband transport medium, suchas a coaxial cable.

DAS 100 comprises a digital DAS transport meaning that the downlink anduplink transport signals transmitted between host unit 102 and remoteunits 106 over communication links 130 are generated by digitizing thedownlink and uplink RF signals, respectively. In other words, thedownlink and uplink transport signals are not analog RF signals butinstead are digital data signals representing digital RF samples of amodulated RF signal. These digital data signals, which may bealternately referred to herein as “digital RF”, “digitally sampled RF”and “digital baseband”, may comprise digital representations of an RF,IF or baseband version of the original RF signal. Further, these samplesmay be defined as real samples, or as pairs of complex (IQ orquadrature) samples. For example, if a particular communication signaldestined for transmission to subscriber unit 108 is a modulated RFsignal in the 900 MHz band, then host unit 102 will generate basebanddigital samples of the modulated 900 MHz RF signal from BTS 110, whichare then distributed by host unit 102 to the remote units 106.Alternatively, an all-digital BTS may generate baseband digital samplesdirectly. At the remote units, the digital samples of the modulated RFsignal are converted from digital into an analog RF signal to bewirelessly radiated from the antennas 107. In the uplink analog RFsignals received at remote unit 106 are digitally sampled to generatedigital RF data samples for the uplink transport signals. BTS 110, hostunit 102 and remote units 106 each accommodate processing communicationsignals for multiple bands and multiple modulation schemessimultaneously. In the embodiment shown in FIG. 1, each remote unit 106and host unit 102 comprises a digital to analog radio frequencytransceiver (DART) module 132 configured to conserve the availablebandwidth of the communication links 130 by separating and individuallyprocessing spectral regions of interest from a larger RF spectrum. Moredetail regarding the digital to analog radio frequency transceiver(DART) module 132 is provided below.

FIG. 2 is a block diagram of one embodiment of a remote unit 106. Remoteunit 106 includes a serial radio frequency (SeRF) module 220, a digitalto analog radio frequency transceiver (DART) module 208, a remote DARTinterface board (RDI) 224, and wireless RF components 250 that includeelectronics such as power amplifier, a duplexer, a low noise amplifierand other RF electronics coupled to an antenna 212. In alternateembodiments, SeRF modules and DART modules described herein are realizedusing FPGAs, ASICs, digital signal processing (DSP) boards, or similardevices.

DART module 208 provides bi-directional conversion between analog RFsignals and digital sampled RF for the downlink and uplink transportsignals transmitted between host unit 102 and remote units 106. In theuplink, antenna 212 receives a wireless RF signal from subscriber 208and passes the RF signal to DART module 208 via RF components 250. DARTmodule 208 receives an incoming analog RF signal spectrum and samples apredefined bandwidth of the incoming analog RF signal spectrum at afirst sampling rate to generate digital data for use by SeRF module 220,as described below.

In the downlink, DART module 208 receives digitally sampled RF data fromSeRF module 220, converts the digital RF samples to analog RF, and upconverts the analog RF to a broadcast frequency for wirelesstransmission. After a signal is converted to an analog RF signal by DARTmodule 208, the analog RF signal is sent to RF components 250 forbroadcast via antenna 212. One of ordinary skill in the art upon readingthis specification would appreciate that DART modules may function tooptionally convert the digital RF samples into intermediate frequency(IF) samples instead of, or in addition to, baseband digital samples.

DART modules in a remote unit are specific for a particular frequencyband. A single DART module operates over a defined frequency bandregardless of the modulation technology being used. Thus frequency bandadjustments in a remote unit can be made by replacing a DART modulecovering one frequency band with a DART module covering a differentfrequency band. For example, in one implementation DART module 208 isdesigned to transmit 850 MHz cellular transmissions. As another example,in another implementation DART module 208 transmits 1900 MHz PCSsignals. Some of the other options for a DART module 208 include Nextel800 band, Nextel 900 band, PCS full band, PCS half band, BRS, and theEuropean GSM 900, GSM 1800, and UMTS 2100. By allowing differentvarieties of DART modules 208 to be plugged into RDI 224, remote unit106 is configurable to any of the above frequency bands and technologiesas well as any new technologies or frequency bands that are developed.

SeRF module 220 provides bi-directional conversion between a digitaldata stream and a high speed optical serial data stream. In the uplink,SeRF module 220 receives incoming digital data streams from DART module208 and sends a serial optical data stream over communication link 130to host unit 102. In the downlink, SeRF module 202 receives an opticalserial data stream from host unit 102 and provides a digital data streamto DART module 208. Although FIG. 2 illustrates a single DART modulecoupled to a SeRF module, a single remote unit housing may operate overmultiple bands by possessing multiple DART modules. In one suchembodiment, RDI 224 provides separate connection interfaces allowingeach DART module to communicate RF data samples with SeRF module 220. Inone embodiment a SeRF module actively multiplexes the signals frommultiple DART modules (each DART module processing a different RF band)such that they are sent simultaneously over a single transportcommunication link 130.

FIG. 3 is a block diagram illustrating one embodiment of a host unit102. Host unit 102 is communicatively coupled to multiple remote units106 via the communication links 130, as described with respect toFIG. 1. Host unit 102 includes a host unit digital to analog radiofrequency transceiver (DART) module 308 and a host unit serial radiofrequency (SeRF) module 320. SeRF module 320 provides bi-directionalconversion between digital RF data samples and the multiple high speedoptical serial data streams to and from the remote units 106. In theuplink direction, SeRF module 320 receives incoming serial optical datastreams from a plurality of remote units, extracts from each serialstream the digitized baseband RF data samples corresponding to eachfrequency band, and sums the multiple sample streams for each band intoone composite stream of RF data samples for that band. DART module 308provides a bi-directional interface between SeRF module 320 and one ormore base stations, such as BTS 110. As with remote units 106, when hostunit 320 operates over multiple bands with multiple base stations, aseparate DART module 308 is provided for each frequency band.

As used herein, the terms Host SERF and Host DART refer to SeRF and DARTmodules located in a host unit 102. The terms Remote SeRF and RemoteDART refer to SeRF and DART modules located in a remote unit 106.

FIG. 4A illustrates a digitized RF spectrum 400 that is processed byeither a Host or Remote DART module of one embodiment of the presentinvention. In one embodiment, digitized RF spectrum 400 represents adigital sampling of an uplink analog signal received by a remote unit106. In another embodiment, digitized RF spectrum 400 is instead arepresentation of a downlink signal received at a host unit 102 intendedfor wireless transmission by a remote unit 106. Within spectrum 400,spectral regions 451 and 452 both contain “relevant” RF signals. Thatis, the DART module has been programmed to recognize that spectralregions 451 and 452 contain information to be transported over DAS 100.The first spectral region 451 includes a first bandwidth (BW1) while thesecond spectral region 452 includes a second bandwidth (BW2). Thespectral region 450 corresponds to a non-relevant region of spectrum 400that falls between regions 451 and 452. The DART module is thus notconcerned with the transmission or reception of any signals within thenon-relevant spectral region 450. However, embodiments comprisingmultiple DART modules are contemplated as within the scope of thepresent invention as mentioned above. In one such alternate embodimentof either a remote unit or a host unit, a region defined as non-relevantto a first DART module can be defined as a relevant spectral region to asecond DART module.

FIG. 4B is a block diagram illustrating one embodiment of a mapping ofdigitized RF spectrum 400 onto timeslots of an N timeslot digitaltransport frame 460 carried over communication links 130. Spectralregion is 451 is processed by the DART module for transmission viadigital transport frame 460 by re-sampling that portion of digitized RFspectrum 400 corresponding to spectral region 451. The re-sampling rateused will determine the number of timeslots that will be used totransport spectral region 451 and is based on the size of bandwidth BW1.For example, in one embodiment, three timeslots are required totransport a bandwidth of size BW1. Accordingly, timeslots TS1 (461), TS2(462) and TS3 (463) are allocated for transporting the signals withinspectral region 451.

Similarly, spectral region 451 is processed for transmission via digitaltransport frame 460 by re-sampling that portion of digitized RF spectrum400 corresponding to spectral region 451. The re-sampling rate useddetermines the number of timeslots that will be used to transportspectral region 452 and is based on the bandwidth BW2. As would beapparent to one of ordinary skill in the art upon reading thisspecification, the first sampling rate used for re-sampling spectralregion 451 will likely not be the same as the second sampling rate usedfor re-sampling spectral region 451, unless BW1 and BW2 are similar insize. Continuing the example, assuming that only one timeslot isrequired to transport a bandwidth of size BW2, timeslots TS4 (464) isallocated for transporting the signals within spectral region 452.

As shown by this example embodiment, the signals within the non-relevantspectral region 450 are not mapped onto digital transport frame 460.Thus, timeslots on digital transport frame 460 are not wasted on thisnon-relevant information and may be utilized for other purposes. Forexample, assuming that eight timeslots would otherwise be required tomap the entire bandwidth of digitized RF spectrum 400 onto digitaltransport frame 460, the embodiment described above has reduced thenumber of timeslots needed by four by only mapping the relevant regionsof spectrum 400. In this manner, fewer assigned time slots are requiredto accommodate the digital baseband data than would be if the digitalbaseband data were generated for the non-relevant spectral region 450.This results in bandwidth conservation in the DAS 100.

Although FIG. 2B illustrates spectral regions 451 and 452 mapped toadjacent timeslots of digital transport frame 460, embodiments of thepresent invention do not require adjacent mapping. For example, if TS4(464) was allocated for use by a different DART module, or allocated forother purposes within the DAS 100, then TS5 or any other timeslot withindigital transport frame 460 may be used to transport spectral region352.

As would be apparent to one of ordinary skill in the art upon readingthis specification, the number of distinct regions within a digitized RFspectrum is not limited to only two spectral regions. In other alternateembodiments, three or more spectral regions within a digitized RFspectrum may be defined as carrying relevant signals. The number ofspectral regions that can be handled as discrete signal with a DART willbe limited only by the limits of the implementing hardware.

For example, FIG. 4C illustrates a digitized RF spectrum 470 having fourspectral regions 471, 472, 473 and 474, each containing signals definedas relevant. Regions 475, 476 and 477 are non-relevant regions. In oneembodiment, each of the spectral regions 471, 472, 473 and 474 isindividually re-sampled and mapped to timeslots based on theirrespective bandwidth sizes, as described above for FIG. 4A. In the casewhere the implementing hardware is not configured to re-sample andprocess four spectral regions separately, two or more of the spectralregions may be grouped together to define a single spectral region. Forexample, in FIG. 4C, where regions 471 and 472 contain relevant signalsseparated by a non-relevant region 475, the entire bandwidth includingregions 471, 475 and 472 (shown generally as BW3) may be groupedtogether, re-sampled as a distinct slice of spectrum 470 and assigned totimeslots of frame 460 based on the size of BW3. Using the re-samplingand mapping scheme described in FIGS. 4A-C, a host unit 102 and theremote units 130 communicate RF transport signals that occupy lessbandwidth of the communication links 130 as compared to presentlyexisting schemes because time slots are not assigned for one or morenon-relevant spectral regions.

FIG. 5 is a block diagram illustrating a DART Module 500 of oneembodiment of the present invention. In alternate embodiments, DARTModule 500 may operate as either a Host DART or a Remote DART modulesuch as respective DART Modules 308 and 208. DART module 500 has twomain signal paths; a transmission path 504 and a reception path 506. Forsignals received from a SeRF module, DART module 500 forms paralleldigital RF data from the incoming data stream, if needed, at FPGA 503.In this embodiment, FPGA 503 is a logic device that is programmed toconvert serial digital data into RF sampled data and programmed toconvert RF sampled data into serial digital data. DART module 500 thenconverts the digital RF data to an analog signal with digital to analogconverter (DAC) 508. Transmission path 504 continues with RFtransmission interface 510 which filters, amplifies, and up-converts theanalog signal for RF transmission. As would be readily appreciated byone of ordinary skill in the art upon reading this specification, RFtransmission interface 510 will typically include an assortment offilters, amplifiers, oscillators and attenuators. In one embodiment, thetransmission path exits DART module 500 at a subminiature version A RFcoaxial connector (SMA) connector 520.

In the reception path 506, RF signals are converted from analog todigital and sent to the SeRF module. In one embodiment, analog RFsignals are received at DART module 500 at an SMA connector 525.Reception path 506 includes an RF reception interface 530 thatamplifies, down-converts, and filters the incoming RF signal. As wouldbe readily appreciated by one of ordinary skill in the art upon readingthis specification, RF reception interface 530 will typically include anassortment of filters, amplifiers, oscillators, and attenuators. Afterthe RF reception interface 530, DART module 500 then digitizes thesignal with analog to digital converter 522. FPGA 503 then provides thedata stream as parallel digital RF sampled data to a SeRF module.

FIG. 6 is a block diagram providing further details for FPGA 503 for oneembodiment of the present invention. FPGA 503, for both the upstream anddownstream directions, provides separate signal processing paths foreach discrete spectral region of a digitized RF spectrum (such as 400 or460) that is to be mapped onto timeslots of the transport frame 460.Although the FPGA 503 described in FIG. 6 illustrates an FPGA configuredto process two discrete spectral regions in each direction (illustratedby first and second paths 630,631 in the receive direction and first andsecond paths 632,633 in the transmit direction), one of ordinary skillin the art after reading this specification would appreciate that theFPGA described in FIG. 6 may be scaled upward to include additionalprocessing paths for three or more discrete spectral regions. Thisscaling is limited only by the particular constraints of the underlyinghardware used (for example, the number of available gates provided bythe FPGA hardware selected by the DART equipment designer).

In each direction, FPGA 503 provides a first path for processing digitalsignals associated with the radio frequency signals in a first spectralregion (such as region 451 for example) and a second path for processingdigital signals associated with the radio frequency signals in a secondspectral region (such as region 452, for example). For processing thereception path 506, FPGA 503 includes first conditioning logic 617, afirst digital down converter 625, a second digital down converter 626and a transmitter (TX) 621. For processing the transmission path 504,FPGA 503 includes a receiver (RX) 623, a first digital up converter 628,a second digital up converter 629, summer 650, and second conditioninglogic 619. FPGA 503 further includes a low-voltage differentialsignaling circuit 615 that facilitates communication between thetransmission and receive paths (404, 406) and a SeRF module coupled toDART Module 500. In an alternate embodiment, the first conditioninglogic 617 and the second conditioning logic 619 are realized usingshared conditioning logic.

In the embodiment shown in FIG. 6, FPGA 503 is communicatively coupledto its associated SeRF Module by a bidirectional low-voltagedifferential signaling (LVDS) link 640. A first LVDS lane representedgenerally at 645 and a second LVDS lane represented generally at 646 aresupported. In one implementation of this embodiment, first LVDS lane 645and second LVDS lane 646 each transport digital baseband data at a737.28 Mbps data rate. In this case, the first LVDS lane 645 and secondLVDS lane 646 together transport digital baseband data at a 1474.56 Mbpsdata rate in up to six timeslots of a transport frame 460. In oneembodiment, the link 640 runs at a fixed rate regardless of the payload(i.e., regardless of the number of time slots sent). One of ordinaryskill in the art upon reading this specification would appreciate thatin alternate embodiments of the present invention, the number ofsupported time slots is a design choice based on the number of timeslotssupported by the particular hardware used.

In one embodiment of receive path 506, in operation, ADC 522 receives ananalog RF spectrum from RF reception interface 530 and digitizes thecomplete analog RF spectrum using an initial sampling rate correspondingto the size of the bandwidth of the analog spectrum. The firstconditioning logic 617 receives the digitized data samples from theanalog-to-digital converter 522, and directs the digitized data samplesto digital-down-converters (DDC) 625 and 626. The first digital downconverter 625 and the second digital down converter 626 each receivedigitized data samples of the full RF spectrum.

The first and second digital down converters 625 and 626 are eachconfigured to independently process distinct spectral regions of thesampled RF spectrum. Returning to the example of FIG. 4A, in oneembodiment, first digital down converter 625 is programmed to filter outall signals except those in spectral region 451. For example, in oneembodiment, first digital down converter 625 is programmed with both thecenter frequency of the first spectral region 451 (shown as f_(c1)) andthe bandwidth BW1 of spectral region 451. Digital down converter 625thus applies a band-pass filter to the sampled RF spectrum, allowingonly the data corresponding to the spectral region f_(c1)−½(BW1) tof_(c1)+½(BW1) to pass. Digital down converter 625 then converts the datacorresponding to the first spectral region 451 into digital basebandsignals by re-sampling the data from the initial sampling rate used todigitize the analog RF spectrum to a first sampling rate selected basedon the size of BW1. The first sampling rate will determine the number oftimeslots used to transport the digital baseband signals correspondingto spectral region 451.

In the same way, second digital down converter 626 is programmed withboth the center frequency of the second spectral region 454 (shown asf_(c2)) and the bandwidth BW2 of spectral region 452. Digital downconverter 626 then applies a band-pass filter to the sampled RFspectrum, allowing only the data corresponding to the spectral regionf_(c2)−½(BW2) to f_(c2)+½(BW2) to pass. Digital down converter 626 thenconverts the data corresponding to the second spectral region 452 intodigital baseband signals by re-sampling the data from the initialsampling rate used to digitize the analog RF spectrum to a secondsampling rate selected based on the size of BW2. The second samplingrate will determine the number of timeslots used to transport thedigital baseband signals corresponding to spectral region 452.

Serialized transmitter (TX) 621 is positioned to receive the first setof digital baseband data samples from the first digital down converter625 at the first sampling rate and the second set of baseband datasample from the second digital down converter 626 at the second samplingrate. Transmitter 621 multiplexes and serializes these two sets ofbaseband data into timeslots and provides the serialized data to theSeRF Module via the low-voltage differential signaling circuit 615.

In one embodiment of transmit path 506, in operation, DART Module 500receives digital baseband data from the SeRF module via the low-voltagedifferential signaling circuit 615. Serialized receiver 623 ispositioned to receive serialized input from the low-voltage differentialsignaling circuit 615 and to direct data from timeslots associated withthe first spectral region 451 to the first digital up converter 628, anddata from timeslots associated with the first spectral region 451 to thesecond digital up converter 629. The first digital up converter 628receives the data from timeslots associated with the first spectralregion 451 at the first sampling rate and up-converts the baseband databy re-sampling the data from the first sampling rate to an outputsampling rate. The second digital up converter 629 receives the datafrom timeslots associated with the second spectral region 452 at thesecond sampling rate and up-converts the baseband data by re-samplingthe data from the second sampling rate to the same output sampling rateused by first digital up converter 628. By upconverting both sets ofbaseband data to the same output sample rate, the up-converted datasample output from both digital upconverters 628, 629 can be readilysummed together for further processing by DART Module 500 as a singledata signal. Accordingly, summer 650 sums the upconverted data sampleoutputs from digital upconverters 628, 629 and provides the summedsignal to DAC 508 via 2^(nd) conditioning Logic 619.

Because FPGA 503 is a field programmable device, it can be adjusted tomeet changing needs of the end user. For example, the center frequenciesf_(c1) and f_(c2) can be reprogrammed into FPGA 503 in order to shiftthe locations of spectral regions 451 and 452 within spectrum 400.Similarly BW1 and BW2 may be adjusted to accommodate larger or narrowerbandwidths. The number and/or position of timeslots within frame 460provisioned for each discrete spectral region can also be reconfigured.As mentioned previously, the number of individual signal paths forhandling additional spectral regions may be increased by configuring theFPGA with additional digital up converters and digital down converters.In one embodiment, a plurality of predefined configuration builds arestored in a memory, for example within a SeRF Module. In such anembodiment, a DART Module's FPGA can be reconfigured by pushing a newbuild image onto the FPGA.

FIG. 7 is a flow diagram a method 700 of one embodiment of the presentinvention. The method begins at 702 with receiving configurationinformation, the configuration information identifying a plurality ofrelevant spectral regions within an RF spectrum. In one embodiment, eachrelevant spectral region is identified by a center frequency andbandwidth. The relevant spectral regions are indicative of separateradio frequency bands of interest that are to be transported via adigital DAS. Configuration information can also information regardingthe number and position of timeslots available for allocation to eachspectral region. In one embodiment, the configuration information may bereceived via a user interface either directly or indirectly coupled tothe DART module. The method proceeds to 704 with selecting a build froma plurality of builds stored in a data storage device, such as but notlimited to a flash memory. Selection of the build is based on thereceived configuration information. The method proceeds to 706 withprogramming a field programmable device, such as an FPGA, bytransferring the build to the field programmable device. Although theexample of an FPGA has been used in this specification, other fieldprogrammable devices are contemplated as within the scope of embodimentsof the present invention.

FIG. 8 is a flow chart illustrating a method 800 of one embodiment ofthe present invention. The method begins at 802 with receiving digitalsamples of an RF spectrum sampled at an initial sampling rate. The RFspectrum comprises a first spectral region that includes signals ofinterest and a second spectral region that includes signals of interest.In one embodiment, the first and second spectral regions are separatedby a non-relevant spectral region. The method proceeds to 804 and 806,which occur in parallel. At 804 the method proceeds with generating afirst set of digital baseband data of the first spectral region at afirst sampling rate using a first signal path. At 806 the methodproceeds with generating a second set of digital baseband data of thesecond spectral region at a second sampling rate using a second signalpath. As described above, the first sampling rate and the secondsampling rate are determined from the bandwidths of the first spectralregion and second spectral regions, respectively. The first signal pathcomprises a first digital down converter that filters the RF spectrum topass only data signals corresponding to the first spectral region. Thosedata signals are then re-sampled to the first sampling rate, which willdetermine the number of timeslots the first set of digital baseband datawill occupy on the transport frame. The second signal path comprises asecond digital down converter that filters the RF spectrum to pass onlydata signals corresponding to the second spectral region. Those datasignals are then re-sampled to the second sampling rate, which willdetermine the number of timeslots the second set of digital basebanddata will occupy on the transport frame.

The method then proceeds to 808 where the first and second sets ofdigital baseband data are multiplexed into a serial data stream byassigning the first set of digital baseband signals to a first set oftimeslots of a transport frame and the second set of digital basebandsignals to a second set of timeslots of the transport frame. The methodproceeds to 810 with transmitting the transport frame. As would beappreciated by one of ordinary skill in the art, by processing the firstand second spectral regions separately and at sample times correspondingto their respective bandwidths, the total number of timeslots necessaryto transport the signals is less than if the entire received RF spectrumwas converted to baseband and assigned to timeslots. In one embodiment,transmitting the transport frame comprises a SeRF Module transmittingthe transport frame via an optical fiber. In the case where this methodis implemented at a host unit, the transport frame is transmitted viathe Host SeRF Module to a remote unit. In the case where this method isimplemented at a remote unit, the transport frame is transmitted via theRemote SeRF Module to the host unit.

FIG. 9 is a flow diagram of a method 900 of one embodiment of thepresent. The method begins at 902 with receiving an input transportsignal comprising a transport frame having a plurality of timeslots. Themethod proceeds to 904 with parsing the input transport signal into atleast a first set of baseband signal and a second set of basebandsignals based on a timeslot configuration of the input transport signal.In one embodiment, demultiplexing logic in the low-voltage differentialsignaling circuit parses the input stream and sends the baseband data toeither a first digital up converter or second digital up converter basedon the timeslot configuration. The method then proceeds to blocks 906and 908, which run in parallel.

At block 906, the method proceeds with upconverting the first set ofbaseband signals from a first sampling rate to an output sampling rate.At block 908 the method proceeds with upconverting the second set ofbaseband signals from a second sampling rate to an output sampling rate.By upconverting both sets of baseband data to the same output samplerate, the up-converted data sample output from both digital upconverterscan be readily summed together into a single signal of data samples.Accordingly, the method proceeds to 910 with summing the upconvertedfirst set of baseband signals with the upconverted second set ofbaseband signals to produce a set of output data samples. The methodthen proceeds to 912 with converting the set of output data samples toan analog RF signal through a digital-to-analog converter.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. This disclosure isintended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

1. A digital-analog radio transceiver for providing digital transport ofsignals on a radio-frequency (RF) distributed antennal system, thetransceiver comprising: a receive path circuit including an RF receptioninterface coupled to an analog-to-digital converter, theanalog-to-digital converter receiving a down-converted analog RFspectrum from the RF reception interface and producing a digitized RFspectrum at an input sampling rate; a logic device coupled to thereceive path circuit and receiving the digitized RF spectrum at theinput sampling rate, the logic device producing a first set of basebanddata samples at a first sampling rate, the first set of baseband datasamples corresponding to a first spectral region of the analog RFspectrum, the logic device further producing a second set of basebanddata samples at a second sampling rate, the second set of baseband datasamples corresponding to a second spectral region of the analog RFspectrum; wherein the logic device maps the first set of baseband datasamples at the first sampling rate to a first set of timeslots of aserial data stream transport frame and maps the second set of basebanddata samples at the second sampling rate to a second set of timeslots ofthe transport frame.
 2. The transceiver of claim 1, wherein the firstset of timeslots consists of a first number of timeslots based on abandwidth of the first spectral region and the second set of timeslotsconsists of a second number of timeslots based on a bandwidth of thesecond spectral region.
 3. The transceiver of claim 1, wherein theanalog RF spectrum comprises a third spectral region between the firstspectral region and the second spectral region, wherein data from thethird spectral region is not mapped onto timeslots of the transportframe.
 4. The transceiver of claim 1, the logic device including atleast a first digital down converter and a second digital downconverter, the first digital down converter and the second digitaloperating in parallel and each receiving the digitized RF spectrum atthe input sampling rate; the first digital down converter convertingdata corresponding to the first spectral region of the analog RFspectrum into the first set of digital baseband data at the firstsampling rate, where the first sampling rate is a function of a size ofa bandwidth of the first spectral region; the second digital downconverter converting data corresponding to the second spectral region ofthe analog RF spectrum into the second set of digital baseband data atthe second sampling rate, where the second sampling rate is a functionof a size of a bandwidth of the second spectral region.
 5. Thetransceiver of claim 4, the logic device further comprising a serializedtransmitter receiving the first set of digital baseband data at thefirst sampling rate and the second set of digital baseband data at thesecond sampling rate and mapping the first set of digital baseband datato the first set of timeslots and the second set of digital basebanddata to the second set of timeslots.
 6. The transceiver of claim 1,further comprising: a transmission path circuit including an RFtransmission interface coupled to an digital-to-analog converter; thelogic device further coupled to the transmission path circuit, the logicdevice receiving an input transport frame having a plurality oftimeslots, wherein a first set of the plurality of timeslots includes athird set of baseband data samples at the first sampling rate, the thirdset of baseband data samples corresponding to the first spectral regionof the analog RF spectrum, and wherein a second set of the plurality oftimeslots includes a fourth set of baseband data samples at the secondsampling rate, the fourth set of baseband data samples corresponding tothe second spectral region of the analog RF spectrum; wherein the logicdevice up-converts the third set of baseband data samples at the firstsampling rate to a first set of RF data samples corresponding to thefirst spectral region at an output sampling rate; wherein the logicdevice up-converts the fourth set of baseband data samples at the secondsampling rate to second set of RF data samples corresponding to thesecond spectral region at the output sampling rate; wherein the logicdevice sums the first set of RF data samples with the second set of RFdata samples to produce a set of output data samples at the outputsampling rate; wherein the digital-to-analog converter receives theoutput data samples at the output sampling rate and generates an outputanalog signal from the output data samples; wherein the RF transmissioninterface receives the output analog signal and up-converts the outputanalog signal into an analog RF signal within the analog RF spectrum. 7.The transceiver of claim 6, the logic device including at least a firstdigital up converter and a second digital up converter, the firstdigital up converter and the second digital up converter operating inparallel, the first digital up converter receiving the third set ofdigital baseband signals and converting the third set of digitalbaseband signals into the first set of RF data samples corresponding tothe first spectral region of the analog RF spectrum at the outputsampling rate; the second digital up converter receiving the fourth setof digital baseband samples and converting the third set of digitalbaseband signals into the second set of RF data samples corresponding tothe second spectral region of the analog RF spectrum at the outputsampling rate.
 8. The transceiver of claim 7, the logic device furthercomprising a serialized receiver receiving the input transport frame andparsing timeslots of the transport frame to the first digital upconverter and the second digital up converter based on a timeslotconfiguration of the input transport frame.
 9. The transceiver of claim6, wherein the analog RF spectrum comprises a third spectral regionbetween the first spectral region and the second spectral region,wherein data from the third spectral region is not mapped onto timeslotsof the input transport frame.
 10. The transceiver of claim 1, whereinthe logic circuit comprises a field programmable device.
 11. Thetransceiver of claim 1, wherein the first spectral region and secondspectral region are user selectable from a plurality of pre-built logiccircuit configurations.
 12. The transceiver of claim 1, wherein a centerfrequency and bandwidth size that define the first spectral bandwidthare user reconfigurable.
 13. A digital-analog radio transceiver forproviding digital transport of signals on a radio-frequency (RF)distributed antennal system, the transceiver comprising: a transmissionpath circuit including an RF transmission interface coupled to andigital-to-analog converter; a logic device further coupled to thetransmission path circuit, the logic device receiving an input transportframe having a plurality of timeslots, wherein a first set of theplurality of timeslots includes a first set of baseband data samples atfirst sampling rate, the third set of baseband data samplescorresponding to a first spectral region of an analog RF spectrum, andwherein a second set of the plurality of timeslots includes a second setof baseband data samples at a second sampling rate, the second set ofbaseband data samples corresponding to a second spectral region of theanalog RF spectrum; wherein the logic device up-converts the first setof baseband data samples at the first sampling rate to a first set of RFdata samples corresponding to the first spectral region at an outputsampling rate; wherein the logic device up-converts the second set ofbaseband data samples at the second sampling rate to second set of RFdata samples corresponding to the second spectral region at the outputsampling rate; wherein the logic device sums the first set of RF datasamples with the second set of RF data samples to produce a set ofoutput data samples at the output sampling rate; wherein thedigital-to-analog converter receives the output data samples at theoutput sampling rate and generates an output analog signal from theoutput data samples; wherein the RF transmission interface receives theoutput analog signal and up-converts the output analog signal into ananalog RF signal within the analog RF spectrum.
 14. The transceiver ofclaim 13, wherein the analog RF spectrum comprises a third spectralregion between the first spectral region and the second spectral region,wherein data from the third spectral region is not mapped onto timeslotsof the input transport frame.
 15. A method for providing digitaltransport of signals on a radio-frequency (RF) distributed antennalsystem, the method comprising: receiving digital samples of an analog RFspectrum sampled at an initial sampling rate; generating a first set ofdigital baseband data of the first spectral region at a first samplingrate; in parallel with generating the first set of digital basebanddata, generating a second set of digital baseband data of the secondspectral region at a second sampling rate; multiplexing the first set ofdigital baseband data and the second set of digital baseband data into aserial data stream by assigning the first set of digital basebandsignals to a first set of timeslots of a transport frame and the secondset of digital baseband signals to a second set of timeslots of thetransport frame; and transmitting the transport frame.
 16. The method ofclaim 15, wherein the first sampling rate is determined from a bandwidthsize of the first spectral region and the second sampling rate isdetermined from a bandwidth size of the second spectral region.
 17. Themethod of claim 15, wherein generating the first set of digital basebanddata of the first spectral region further comprises filtering thedigital samples of the analog RF spectrum to pass only data signalscorresponding to the first spectral region; and wherein generating thesecond set of digital baseband data of the second spectral regionfurther comprises filtering the digital samples of the RF spectrum topass only data signals corresponding to the second spectral region. 18.The method of claim 15, wherein the first set of timeslots consists of afirst number of timeslots based on a bandwidth of the first spectralregion and the second set of timeslots consists of a second number oftimeslots based on a bandwidth of the second spectral region.
 19. Themethod of claim 15, wherein the analog RF spectrum comprises a thirdspectral region between the first spectral region and the secondspectral region, wherein data from the third spectral region is notmapped onto timeslots of the transport frame.
 20. The method of claim15, further comprising: receiving configuration information, theconfiguration information identifying a plurality of relevant spectralregions within the analog RF spectrum; selecting a build from aplurality of builds stored in a data storage device based on theconfiguration information; and programming a field programmable deviceby transferring the build to the field programmable device.
 21. Themethod of claim 20, wherein the configuration information identifies acenter frequency and bandwidth size for defining the first spectralregion.
 22. A method for providing digital transport of signals on aradio-frequency (RF) distributed antennal system, the method comprising:receiving an input transport signal comprising a transport frame havinga plurality of timeslots; parsing the input transport signal into atleast a first set of baseband signal and a second set of basebandsignals based on a timeslot configuration of the input transport signal;upconverting the first set of baseband signals from a first samplingrate to an output sampling rate; in parallel with upconverting the firstset of baseband signals, upconverting the second set of baseband signalsfrom a second sampling rate to the output sampling rate; summing theupconverted first set of baseband signals with the upconverted secondset of baseband signals to produce a set of output data samples; andconverting the set of output data samples to an analog RF signal througha digital-to-analog converter.
 23. The method of claim 22, whereinupconverting the first set of baseband signals further comprisesgenerating a first set of RF data samples corresponding to a firstspectral region of an analog RF spectrum; and wherein upconverting thesecond set of baseband signals further comprises generating a second setof RF data samples corresponding to a second spectral region of theanalog RF spectrum;
 24. The method of claim 23, wherein the analog RFspectrum comprises a third spectral region between the first spectralregion and the second spectral region, wherein data from the thirdspectral region is not mapped onto timeslots of the input transportframe.
 25. The method of claim 22, wherein the timeslot configuration ofthe input transport signal comprises a first set of timeslots consistingof a first number timeslots corresponding to a bandwidth of the firstspectral region and a second set of timeslots consisting of a secondnumber of timeslots corresponding to a bandwidth of the second spectralregion.
 26. The method of claim 22, further comprising: receivingconfiguration information, the configuration information identifying aplurality of relevant spectral regions within an analog RF spectrum;selecting a build from a plurality of builds stored in a data storagedevice based on the configuration information; and programming a fieldprogrammable device by transferring the build to the field programmabledevice.
 27. The method of claim 26, wherein the configurationinformation identifies a center frequency and bandwidth size fordefining a first spectral region.